Wednesday 13 July 2011 10.22 EDT
First published on Wednesday 13 July 2011 10.22 EDT

The timing was uncanny. Last Wednesday, after weeks of planning, a campaign group called Hacked Off was launched at an event in the House of Lords. Formed by a group of lawyers, journalists and academics, the plan was to lobby for a full, judge-led inquiry into the hacking allegations that the Guardian had been covering for some years.

They couldn't have known that just 48 hours before their planned launch, the biggest scandal in press history was to erupt.

The campaign group is made up of a mixture of experts and victims of hacking, including the family of the murdered schoolgirl Milly Dowler, the actor Hugh Grant and the ex-Met senior police officer Brian Paddick; the charity run by Sara Payne has offered support.

Hacked Off was set up by Martin Moore, director of the Media Standards Trust, and Brian Cathcart, former deputy editor of the Independent and now professor of journalism at Kingston University. Its advisory committee includes some of the biggest names in the hacking story, the Labour MPs who have tirelessly campaigned on hacking, including Tom Watson, and the former Lib Dem MP Evan Harris, who is influential in the party's grassroots.

Mark Lewis, the lawyer representing the Dowler family, is also at the heart of the operation. Among those attending the campaign launch were the former deputy prime minister John Prescott, the Tory grandee Norman Fowler, the human rights lawyer Helena Kennedy, the senior Labour politicians Charles Falconer and Tessa Jowell, the philosopher Onora O'Neill, the associate editor of the Independent Jemima Khan and ex-formula one boss Max Moseley. Its petition for a full inquiry into hacking has nearly 8,000 signatories.

Hacked Off runs out of the offices of the Media Standards Trust and most staff are working for free with only one, part-time, paid coordinator. It has rushed to set up a fund-raising scheme and so far it has had one significant donation, from Hugh Grant, but has been overtaken by events. Its argument for a full public inquiry has been propelled to centre stage of the scandal after David Cameron announced that one would indeed go ahead.

"We changed tack," says Moore. "The commitment had been made but we know that inquiries without the right remit can be as frustrating and ineffective as no inquiry." The group set about trying to ensure that the inquiry would get to the bottom of the scandal.

They approached the party leaders to set up meetings with the Dowler family, Paddick and members of the campaign. By Friday Nick Clegg had agreed, by Saturday Ed Miliband was on board, and by Sunday the prime minister's office was in.

At the Clegg and Miliband meetings this week, campaigners pushed hard for the broadest possible inquiry, covering politicians as well as the police and the press. They gave the same message to the three chairs of the select committees involved.

Their concern was that there could be an attempt to hive off the element that examined press regulation – and the relationships between press barons and politicians – into a second-rate inquiry, separate from the main one into hacking, which would be led by a judge.

On Tuesday, Grant gave interviews to the Guardian and Newsnight issuing a direct challenge: "This is a watershed moment for David Cameron and his government. He can either continue to be Murdoch's little helper or he can be a statesman. If it's the latter, he needs to announce a wider inquiry. It must cover the press, police and politicians."

It now appears that their message was received by Clegg and Miliband – and the select committee chairs – who all went into their meetings with Cameron arguing for a similar broad remit for the inquiry. For a campaign that is less than a week old it appears to have already affected the course of the judicial processes.

The campaign will now pay close attention to the inquiry, highlighting where it is falling short and ensuring that both victims and experts have a proper voice in it.

Moore said: "At some point I will sit back and try and look back on this week. It has been very hectic and quite surreal – and it's not finished yet."